1. Field of the Invention
The present invention relates to a cushioning device for a piston and cylinder device and, more specifically, to an expandable cushion pluger for use in decelerating a piston at the end of its stroke. A feature is also provided to permit more rapid break away of the piston on its return stroke.
2. Description of the Prior Art
It is common practice to utilize cushioning devices in a piston and cylinder device to prevent high velocity contact of the piston and cylinder head. Such cushioning devices, such as described in U.S. Pat. No. 2,755,775, utilize a cushion sleeve, which restricts the passage of fluid into an exit port. Such restriction causes back pressure on the piston, thereby slowing it at the end of its stroke. However, it has been found that such cushioning devices provide deceleration only until the piston has traveled to within a very short distance of the cylinder head. At this point, it was found that the piston speeded up, thereby permitting the piston to slam against the cylinder head. This phenomenon was due to the fact that pressures within the cylinder were rapidly rising due to the restriction of fluid flow out of the exit port, while the area for escape was such as to allow increased flow rate and piston increased speed at the very end of the stroke.